Non-destructive testing procedures have heretofore been used in conjunction with the processing of metal parts or the like to detect defective parts, to avoid unnecessary and expensive processing of defective parts and to otherwise obtain very important advantages. In the processing of steel billets, for example, the magnetic particle inspection method has been used to detect defects prior to the performance of expensive subsequent processing operations on the billet. With the magnetic particle inspection method, finely divided particles, usually in a liquid carrier, are applied over the surface of the billet during or after magnetization of the billet, the particles being concentrated over any leakage fields produced by surface or subsurface cracks or defects. When cracks are indicated by the magnetic particle inspection, the affected portion of the billet is ground away so that the billet is free of the defect in subsequent processing operations.
Although highly advantageous, such procedures still leave something to be desired in that the grinding operation must be carefully performed and it takes a substantial length of time for an operator to process a billet which has a considerable number of indicated defects.